System Packet Interface

The System Packet Interface (SPI) family of Interoperability Agreements from the Optical Internetworking Forum specify chip-to-chip, channelized, packet interfaces commonly used in synchronous optical networking and Ethernet applications. A typical application of such a packet level interface is between a framer (for optical network) or a MAC (for IP network) and a network processor. Another application of this interface might be between a packet processor ASIC and a traffic manager device.

There are two broad categories of chip-to-chip interfaces. The first, exemplified by PCI-Express and HyperTransport, supports reads and writes of memory addresses. The second broad category carries user packets over 1 or more channels and is exemplified by the IEEE 802.3 family of Media Independent Interfaces and the Optical Internetworking Forum family of System Packet Interfaces. Of these last two, the family of System Packet Interfaces is optimized to carry user packets from many channels. The family of System Packet Interfaces is the most important packet-oriented, chip-to-chip interface family used between devices in the Packet over SONET and Optical Transport Network, which are the principal protocols used to carry the internet between cities.

The agreements are:

These agreements grew out of the donation to the OIF by PMC-Sierra of the POS-PHY interface definitions PL-3 and PL-4, which themselves came from the ATM Forum's Utopia definitions. These earlier definitions included:

System Packet Interface or SPI as it is widely known is a protocol for packet and cell transfers between PHY and LINK layer devices in multi-gigabit applications. This protocol has been developed by Optical Internetworking Forum (OIF) and is fast emerging as one of the most important integration standards in the history of telecommunications and data networking. Devices implementing SPI are typically specified with line rates of 700~800 Mbit/s and in some cases up to 1 Gbit/s. The latest version is SPI 4 Phase 2 also known as SPI 4.2 delivers bandwidth of up to 16 Gbit/s for a 16 bit interface.

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